1. Field of Invention
The invention relates to wastewater treatment systems using ponds or lagoons as holding areas and for biological treatment of sewage, industrial and agricultural wastewater and the like.
2. Description of Prior Art
Conventional sewage treatment processes, which have proven adequate with no major design changes for many years, are now recognized as inadequate to meet the present Federal water pollution control regulations and other developing standards without extensive modification, additions and high construction costs. Such conventional systems are also costly to operate, have high electrical demands, and consume precious natural resources, including fossil fuels, chemicals and water. Such processes are inadequate of removing or detoxifying the majority of the most harmful components of modern day wastewater, e.g., pesticides, herbicides, phenols, heavy metals, and a host of complex domestic and industrial chemicals now recognized as potentially carcinogenic. Moreover, existing systems were not designed or intended to fulfill the pressing need for reclaiming for re-use the large quantities of water which are currently being discharged into the oceans, rivers, streams, and the like. Conventional sewage treatment processes, such as trickling filters or activated sludge, are dependent on the growth, survival, productivity, and harvesting of bacteria to provide treatment. However, these systems are essentially a monoculture, e.g., bacteria only, and are inherently less stable and efficient than multi-species, polyculture systems containing a variety of bacteria, invertebrates, and sludge grazers, algae, plants, and the like. A recent study by the U.S. Environmental Protection Agency, "Economic Assessment of Wastewater Aquaculture Treatment Systems" (Upton B. Henderson and Frank S. Wert, Environmental Protection Agency Report No. 600/2-76-293, 1976), evaluated eleven different aquaculture-type treatment systems utilizing polyculture lagoons containing a variety of aquatic plants, algae, invertebrates and fish. These were compared to three different conventional treatment methods (activated sludge, trickling filters, etc.) and in all cases the aquaculture systems reduced projected treatment costs as much as 94% of conventional technology methods.
In recent years, ecological-type lagoon wastewater systems using balanced food chain organisms have proven successful at capturing nutrients, concentrating chemicals, metabolizing organic compounds, detoxifying dangerous synthetic chemicals, and eliminating pathogenic bacteria and viruses. A few of the more interesting projects in the U.S. are summarized as follows:
Mississippi. Research by the National Aeronautics and Space Administration in Bay St. Louis, Mississippi, has recently demonstrated that one acre of water hyacinths can remove over 3,500 pounds of nitrogen and 800 pounds of phosphorus per year, as well as remove and metabolize over 18,000 pounds of phenol, a toxic organic pollutant, and absorb 44,000 gm. of trace heavy metals per acre per year, see the article, "Application of Vascular Aquatic Plants for Pollution Removal, Energy and Food Production in a Biological System" (B. C. Wolverton, R. M. Barlow and R. C. McDonald, Biological Control of Water Pollution, J. Tourbier and R. Pierson, eds., pp. 141-149, 1976).
Texas. The Texas Department of Health Resources and the City of Austin have operated a small, 4-pond (0.14 ac. total) wastewater treatment system which utilizes a combination of water hyacinths, other vascular aquatic plants, micro-invertebrates and fish and shrimp to concentrate the sewage nutrients into an easier harvest form. The ecological system has been operated for 18 months in various modes and has shown the ability to reduce the throughput BOD.sub.5 by 97%, suspended solids by 95%, total nitrogen by 65%, and phosphorus by 20%. Fecal coliforms have also been reduced 98% through the natural biological processes, see article, "Water Hyacinth Culture for Wastewater Treatment" (Ray Dinges, Texas Department of Health Resources, Division of Wastewater Technology and Surveillance, Austin, Texas, 1976).
Oklahoma. The Oklahoma Department of Health has operated for 18 months a series of six, 6.5-acre waste treatment lagoons. The last four acres were stocked with a polyculture of fishes, including channel catfish, fat-head minnows, golden shiners, and Tilapia. The fish feed on the micro-invertebrates which in turn feed on the luxuriant growth of algae generated by the sewage nutrients. The quality of effluent from this food chain proved to be far superior to effluent from the same system operated without the fish present. Analysis of water samples from the third through sixth cells, and 179 samples of fish flesh, taken over the course of the study showed no presence of pathogenic virus or bacteria in any of the samples, even though no chlorination of the original raw sewage was made, see article, "Aquaculture as an Alternative Treatment System" (R. Leroy Carpenter, Mark S. Coleman, and Ron Jarman, Biological Control of Water Pollution, J. Tourbier and R. Pierson, eds., pp. 215-224, 1976).
Michigan. In Michigan 2 MGD of secondary effluent is being treated in an intensely managed aquatic and terrestrial nutrient recycling system consisting of 38 acres of lakes, 3 acres of marsh, and 314 acres of irrigated land. The effluent from the system exceeds all Federal Standards for reuse. In Muskegon County, Michigan, 27 MGD of effluent is applied to 11,000 acres of land, 4,500 acres of which are planted to corn. The corn yields are about twice the county average, and revenues from their sale reduce waste treatment costs to only 24.cent./1,000 gallons. See following articles: "Utilization of Natural Ecosystems for Wastewater Renovation," Kenneth R. Voight, Institute of Water Research, Michigan State University, Report No. Y005065, 1976; "Wastewater: Is Muskegon County's Solution Your Solution?", John S. Walker, Environmental Protection Agency Report No. 905/2-76-004, 1976.
Long Island. A marsh/pond system in Long Island, stocked with natural marsh plants, fish, invertebrates, and attracting numerous wildfowl and game, has been continously receiving 10,000 gallons per day of raw sewage for three years. Operating through all seasons and with widely fluctuating loads, the effluent has always achieved potable quality and is used for groundwater recharge by natural percolation, see article, "Meadow/Marsh Systems as Sewage Treatment Plants" (Maxwell M. Small, Brookhaven National Laboratory, New York, NTIS Report No. BNL-20757, 1975).
California. The Los Alisos Water District in Orange County has disbanded a relatively new, but troublesome conventional activated sludge plant in favor of four well managed aerated lagoons. The 1.6 MGD effluent is totally recycled for farming of barley, tomatoes and peppers, irrigation of a commercial sod farm, and land application. The percolated effluent from the land application is then collected in holding reservoirs and will be used to maintain a beautiful lake for boating and swimming by the same families that produced the sewage. User costs have been reduced by the sale of effluent and the district is totally self-supporting without government funds.
In spite of the increased treatment efficiency of lagoons using improved techniques, most ecological lagoon systems such as listed above still suffer from the lack of reliability due to seasonal fluctuations and excessive land requirements.